Effect of ball milling energy and carbon content on electrochemical properties of FeF3/acetylene black composites for high-capacity thermal battery

Abstract

Recently, there has been an increasing demand for high-voltage thermal batteries. FeF3 has a high open-circuit voltage of 2.7 V and is gaining attention as a potential alternative. However, it involves the problem of a low electrical conductivity owing to the wide band gap (5.96 eV) and the generation of lithium fluoride (LiF), which is a discharge product in the conversion reaction. To address this issue, acetylene black with high conductivity is utilized to enhance the electrochemical activity of metal fluoride (FeF3). At present, FeF3/AB is produced by low- and high-collision-energy ball milling. These are mechanical milling methods that involve different collision energies. High-collision-energy ball milling has been demonstrated to degrade the electrochemical performance owing to crystal deformation. In contrast, low-collision-energy ball milling has demonstrated the potential for application in thermal batteries by minimizing crystal deformation and enhancing the electrical conductivity. In this study, the amount of added carbon was optimized to enhance the performance of thermal battery materials. Both low- and high-collision-energy ball-milling processes exhibited remarkable thermal stability when 5.0 wt% carbon was added. However, the high-collision-energy ball-milling process did not effectively enhance the thermal cell performance because the electrical conductivity did not increase significantly. Therefore, FeF3/5.0 wt% AB produced by low-collision-energy ball milling exhibited remarkable thermal stability and electrical conductivity. This indicates its potential for use in thermal batteries.